Which ephone-dn can join the hunt group whenever a wild card slot becomes available?

Refer to the exhibit.

Which ephone-dn can join the hunt group whenever a wild card slot becomes available?

A.
ephone-dn 1

B.
ephone-dn 2

C.
ephone-dn 3

D.
ephone-dn 4

E.
ephone-dn 6